After a repair of broken screw posts my HP-41CX (coconut) runs very satisfying, almost without any problem. (I can’t say if the below mentioned problem existed before, I haven’t used the CX for years).
BUT - the time in the CX runs much faster than it should. One minute standard earth time means 2:56 minutes in the CX universe. With this big delta to the real time the Correct function does not help. Did anyone come across this problem? Does anybody have a hint what can be the reason?
All commands of the Timer Module U11 work correct, no problem at all (Date, CLKT, DDAYS, etc.), thus I hope that the problem is outside of the U11 (HP Part Number 01LF6-0001).
The Timer U11 uses a crystal / quartz Y1 with a parallel switched resistor R4 (22 MΩ).
Has anybody seen a specification of the Quartz/Crystal (HP Part Number 0410-1381)?
In the Service Manual nothing is mentioned.
My assumption is that the crystal and R4 are part of an oscillator that provides time information, mainly build into U11, the Timer Module but the quartz could not be integrated into U11.
What can make this oscillator run three times faster than nominal, is it running on an overtone due to aging ?
About one week later - Problem is solved!
Waiting for the ordered and not yet delivered components (Y2 and R4), I refurbished my card reader ("gummy wheel problem“) in the meantime.
I put the refurbished Card Reader in the CX; The reader was listed in Catalog 1, so far so good.
When I put a first card in the reader the power sucked by the engine led the CX lost its memory. The reader needed 2, 3 attempts before the cards could be read without problems.
The clock in the CX, which ran 3 times faster than it should since I reassembled it, is now running very precisely with the right speed.
The power loss must have reset some internal states in the Timer IC (U11) which became somewhat scrubby in the initial power up phase.